Makhteshim-Agan (UK) is warning farmers that counterfeit parallel imports to its crop protection products could be circulating in the UK.
The company, a global leader in branded generic plant protection products, is investigating reports that a "fake" parallel import of its herbicide Falcon (propaquizafop) contained an illegal substance.
A British farmer ordered Falcon but was sold a parallel import from his buying group after being told his original choice was out of stock.
But when he applied the product to his crops, he observed it was giving off the strong smell of a solvent, and he had doubts over its efficacy.
The product was removed from the farm and taken away for testing by the company and the Health and Safety Executive (HSE).
A spokesman for Makhteshim-Agan said: "Parallel imports are legal, provided they are introduced in line with the parallel trade permit that has been granted.
"In this case, the label on the bottle indicates an old Falcon formulation which is about five years out of date in the UK. We are 99.9% certain that this product was brought in illegally to the UK. Until the tests are completed, we won't know where it has come from."
Samples have been sent to Makhteshim-Agan's production facility in Israel for testing. A HSE spokesman said an investigation was under way but it was "inappropriate to comment further" at this stage.
An NFU spokesman said: "Farmers need to buy pesticides from a reputable source. They need to check that what they order is what they get.
"When they receive products, they should check the labelling. Is it in English? When they open it, does it smell and look the same?"
Chris Sambrook, a PhD researcher at Harper Adams University, is researching the threat that counterfeit pesticides pose to UK agriculture.
He said: "Indications are that as much as 8-10% of pesticides across Europe may be illegal in some shape or form and that counterfeits may account for a significant proportion of this.
"I would hesitate to suggest the UK has this problem to the same extent, but this particular case demonstrates that fake products are certainly reaching the marketplace and I have no doubt they are finding their way to farms."
Propaquizafop is used as a post-emergence herbicide to control annual and perennial grass weeds in oliseed rape, linseed and vegetable crops.
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